(1. 兰州理工大学 省部共建有色金属先进加工与再利用国家重点实验室，兰州 730050；
2. 兰州理工大学 有色金属合金及加工教育部重点实验室，兰州 730050)
摘 要: 采用自孕育法制备A356铝合金半固态浆料，研究薄壁件流变压铸过程中的凝固行为。结果表明：在自孕育制浆过程中，等温保温过程对初生α(Al)颗粒的尺寸和形貌影响较大，而对后续薄壁件压铸过程中的二次凝固组织影响不是很大。当剩余液相充填型腔时，型腔提供的较大冷却速率使剩余液相爆发形核；晶核的生长分为稳定生长和失稳生长两个过程。爆发形核的核心先稳定生长成球状小颗粒，稳定生长的极限尺寸为6.5 μm。由于“成分过冷”等因素的存在，一次凝固(α1)颗粒和二次凝固(α2)颗粒最终均出现不稳定生长现象。由于α1颗粒的存在，剩余液相的成分与原始成分相比更接近共晶成分，导致α2颗粒中Si的含量较α1颗粒中的高。α2颗粒将共晶反应限制在许多晶间小区域内，在较高的局部冷却速率下，共晶硅最终长成细小纤维状或菊花状。
关键字: 铝合金；半固态；自孕育；流变压铸；二次凝固；成分过冷；共晶硅
（1. State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals,
Lanzhou University of Technology, Lanzhou 730050, China;
2. Key Laboratory of Non-ferrous Metal Alloys and Processing, Ministry of Education,
Lanzhou University of Technology, Lanzhou 730050, China）
Abstract:The semisolid slurry of A356 aluminum alloy was prepared by self-inoculation method and the solidification behavior of thin-walled component produced by rheo-diecasting was investigated. The results indicate that the isothermal holding process during slurry preparation has great effect on primary α(Al) particles, but has little effect on the microstructure of secondary solidification in the process of thin-walled rheo-diecasting. When the remaining liquid fills die cavity, due to the large cooling rate provided by metallic dies, the nucleation is expected to take place throughout the entire remaining liquid. The growth of nucleus has two stages, nucleus will grow stably into globular particles with the limited grain size of 6.5 μm, then, as the exist of constitutional undercooling, both primary (α1) particles and secondary (α2) particles will appear unstable growth phenomenon. Compared with original composition of alloy, the remaining liquid closes to the eutectic composition due to the existence of α1 particles, which makes the content of Si in α2 particles higher than that in α1 particles. The eutectic reaction is confined to small intergranular areas due to the presence of fine α2 particles. With high local cooling rate, the eutectic silicon will solidify in fine fibrous or chrysanthemum morphology.
Key words: aluminum alloy; semi-solid forming; self-inoculation method; rheo-diecasting; secondary solidification; constitutional undercooling; eutectic silicon
